The invention disclosed and claimed herein generally pertains to improved apparatus for illuminating film, containing a radiographic or other medical diagnostic image, for viewing and study. More particularly, the invention pertains to apparatus of such type for generating light which illuminates the film with significantly enhanced contrast and resolution, or sharpness, whereby viewability is improved.
View boxes and bright lights are well-known types of devices used by radiologists to view and study radiographic images and other medical diagnostic images which are on film. Such images, showing selected views of body tissue, can be obtained by means of conventional X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and other techniques known to those of skill in the medical diagnostic imaging arts. By carefully studying such images, a radiologist can detect the presence of significant medical conditions in a patient or other subject, without the need for invasive surgery. Some important examples of such conditions include breast cancer, lung cancer, pneumonia, fracture, and arthritis.
Conventional view boxes generally are used to view medical diagnostic film, which typically are on the order of 14 inches by 17 inches. Such a device contains one or more fluorescent tubes or other sources of light, and has a front panel typically comprising a translucent light diffuser, such as a sheet of milky white Plexiglas. Also, the dimensions of the front panel may be large enough to accommodate four films, placed side by side, at the same time. Each radiographic imaging film is placed on the light diffuser and transilluminated, for viewing and study, by light from the light source. The light passes through the diffuser and is diffused or scattered thereby. Thus, the light transmitted to the imaging film is of uniform brightness or intensity, so that the imaging film is uniformly illuminated.
If a view box was not provided with a diffuser or other means for scattering light from the fluorescent tube light source, the fluorescent tubes would tend to be seen through the imaging film, interfering with the study thereof. However, the scattering or diffusing of illuminating light causes contrast between lighter and darker regions on the imaging film, as well as resolution, to be degraded from the perspective of an observer. More particularly, because the light which carries the film image to a viewer's eye is diffused, edges or boundaries between lighter and darker regions of the image are blurred, as received on the retina of the viewer. Thus, the radiologist's task of correctly interpreting a film image is made more difficult. Certain conditions, such as breast cancer, lung nodules and small pneumothorax (collapsed lung) are especially hard to detect in any event. If there is too much blurring of edges, or insufficient contrast between lighter and darker areas of a film image, a correct diagnosis of such conditions may not even be possible. The term "resolution," as used herein, means the level of sharpness or blurring which characterizes the boundary, or edge, between adjacent lighter and darker regions of an image.
The importance of providing a high level of contrasted resolution, in illuminating a diagnostic imaging film, is further emphasized by certain regulations of the U.S. government. Under federal law, all X-ray equipment used in the United States for mammography, that is, for acquiring radiographic images for detecting breast cancer, must be periodically tested for contrast and resolution. Such test is conducted by producing a radiographic image of a standardized mammography phantom, which is analyzed by a federal inspector or medical personnel. If the inspector determines that contrast or resolution of the image is insufficient, the facility at which the equipment is located will not be allowed to perform further mammography until the situation is corrected. Such federal standards have been put into place because, if there is insufficient contrast between two adjacent areas of slightly different density in a breast, or insufficient resolution along the edge therebetween, a subtle breast cancer (characterized by an only slightly different density from surrounding normal breast tissue) will not be detectable. This, in turn, may result in a delay of treatment, which could cause great harm to a patient.
In the past, it has been suggested that contrast of a medical diagnostic imaging film, illuminated by means of a view box, could be improved by substantially increasing the spatial separation between the light source and the imaging film. Thus, the light illuminating the film would become less diffused. However, the proposed spatial separation was on the order of six to twelve feet, whereas the depth of a conventional view box is generally less than one foot. It would be highly impractical for a number of reasons, including cost and spatial constraints, to construct a view box having the proposed expanded dimensions.
A bright light is a conventional device for illuminating a small portion of a medical diagnostic film with light of substantially greater intensity than is provided by a view box. Thus, if a radiologist is unsure about the meaning of a portion of a film while studying it on a view box, he can transfer the film to the bright light, and position the film relative thereto, so that the higher intensity light of the bright light will illuminate the unclear film portion. A bright light is particularly useful for studying dark portions of film. Bright lights of the prior art generally comprise a single incandescent bulb of 80-100 watts, and are not provided with a separate diffuser. The light bulb used is generally frosted to provide sufficient diffusion. However, the design of prior art bright lights likewise has generally been unconcerned with providing improved levels of resolution and contrast to film images illuminated thereby.